Last week's TUC conference supported an emergency motion from the CWU, which warned that hundreds of post offices would close and the universal postal service would end if the business was sold off.

BBC: Royal Mail worker

Royal Mail makes a loss on delivering letters and Ofcom, which regulates stamp prices, allowed the price rises because it said the future of the UK's universal, six-day-a-week postal service was "at severe risk" without it.

BBC: Royal Mail faces a spiral of decline, chief executive says

The proposal threatens "the viability of the Postal Service itself, and begin to dismantle the universal network that has served the country well for 200 years, " President Fredric Rolando said.

WSJ: Budget Backs Dropping Saturday Mail Service